In wireless communications, a base station may transmit data to user equipment directly, or through a relay station. The base station may have a cell with a cell identification, and in the cell the user equipment may receive data from the base station. Although the relay station generally does not have a separate cell identification and thus may not create a cell, the relay station may relay data received from the base station to the user equipment.
Traditionally, the base station may transmit to the user equipment data and control information that indicates resource, e.g., time or frequency resource, allocation for the user equipment to receive the data, on different communication channels. For example, according to the Long Term Evolution (LTE) standard, the base station, also known as an Enhanced Node B (eNB) in the LTE standard, may transmit to the user equipment the control information on a physical downlink control channel (PDCCH) and the data on a physical downlink shared channel (PDSCH). Based on the control information received on the PDCCH, the user equipment may determine allocated resources to receive the data on the PDSCH.
The relay station may assist the base station to transmit data to the user equipment by relaying data received from the base station to the user equipment. The base station may transmit to the relay station data to be relayed and control information that indicates resource allocation for the relay station to receive the data to be relayed, on different communication channels. For example, according to the LTE standard, the base station may transmit to the relay station, also known as a relay node (RN) in the LTE standard, the control information on the PDCCH and the data to be relayed on the PDSCH. Based on the control information received on the PDCCH, the relay station may determine allocated resources to receive the data on the PDSCH.
FIG. 1 illustrates a traditional method 100 for the base station to transmit control information to the relay station or the user equipment, according to the LTE standard. Referring to FIG. 1, the base station appends cyclic redundancy check (CRC) parity bits to each of a plurality of pieces of Downlink Control Information, referred to herein as DCIs 102. Each of the DCIs 102 may have a predetermined format according to the LTE standard. The base station then precodes the DCIs each into multiple control channel elements (CCEs) 104. After physical processing, e.g., channel coding, the CCEs may be mapped onto the PDCCH and be transmitted in a subframe 106, based on, e.g., an orthogonal frequency-division multiplexing (OFDM) technique.
The OFDM technique uses a plurality of closely-spaced orthogonal subcarriers to carry data. For example, the data may be allocated on a plurality of parallel data channels, one for each of the subcarriers. Each of the subcarriers may be modulated with a conventional modulation scheme, e.g., quadrature amplitude modulation, at a relatively low symbol rate. In addition, based on the OFDM technique, an inverse fast Fourier transform (IFFT) may be performed on OFDM symbols representing the data on a transmitter side of the OFDM based communication system, and a fast Fourier transform (FFT) may be performed to recover the OFDM symbols on a receiver side of the OFDM based communication system.
Still referring to FIG. 1, the subframe 106 may include N1 OFDM symbols corresponding to one downlink slot and N2 subcarriers. The subframe 106 may also include resource blocks each corresponding to N1 OFDM symbols and N3 subcarriers. Each resource element (k, l) in a resource block corresponds to a time and frequency resource on which data is transmitted.
FIG. 2 illustrates a traditional blind decoding method 200 for the relay station or the user equipment, referred to herein as the receiver, to receive control information from the base station, according to the LTE standard. Referring to FIG. 2, the receiver receives the control information in the form of CCEs 202 on the PDCCH. Due to uncertainty of correspondence between the CCEs 202 and DCIs to be recovered, the receiver may try different lengths, e.g., Length1, Length2, . . . , of candidate DCIs such as a candidate DCI 204. The receiver further descrambles CRC parity bits of the candidate DCI 204. If descrambled CRC parity bits 206 pass CRC check, the candidate DCI 204 is a correctly recovered DCI 208. Otherwise, the receiver may continue to try a different length of candidate DCI for CRC check.